flexive-webdav-webapp: set keytool-maven-plugin version, fix genkey goal invocation

git-svn-id: http://svn.flexive.org/repository/flexive/trunk@2961 d35d4baa-7912-0410-b0ae-edacad209e15
Fix deserialization of old FxValue instances (removed fields), fix exceptions on empty result preferences

git-svn-id: http://svn.flexive.org/repository/flexive/trunk@2962 d35d4baa-7912-0410-b0ae-edacad209e15